1. Field of the Invention
The present invention relates to speed reducing gear technology, and more particularly, to a lubricated harmonic drive.
2. Description of the Related Art
Harmonic drive is a high ratio of gear reducer. A conventional harmonic drive generally comprises a circular spline, a flex spline rotatably mounted within the circular spline, and a wave generator rotatably mounted within the flex spline. After installation of the wave generator in the flex spline, the flex spline is pushed by the outer perimeter of the wave generator and elastically deformed to provide an elliptical shape. Thus, when the wave generator is driven to rotate by a power source, the circular spline and the flex spline are forced to mesh with each other in the major axis of the wave generator and to disengage from each other in the minor axis of the wave generator. Due to a difference in the number of teeth between the circular spline and the flex spline, a high speed reduction ratio will be achieved to provide a high torque output after the wave generator is been continuously rotated.
In order to prolong the lifespan of the harmonic drive and to reduce wear, lubricating designs are created. For example, in the design of U.S. Pat. No. 7,905,326, the lubricating oil allows to go through an oil supply passage in the circular spline into an oil supply hole in the flex spline so that the wave generator can be well lubricated. However, because the flex spline is frequently and elastically deformed during the operation of the harmonic drive, a stress concentration can occur in the area around the oil supply hole, causing structural damage to the flex spline. Further, U.S. Pat. No. 6,672,181 discloses a lubrication mechanism for a wave gear device in which frictionally contacting parts of the external gear and wave generator and frictionally contacting parts on the inside of wave bearing are respectively lubricated using solid lubricants. However, the lubricating performance of solid is not satisfactory.